In a supporting bolt of this type, one end piece consists of a sleeve with a through internal thread, whereby a head, provided with an extension with an external thread, is screwed into one side of the sleeve, while the sleeve has a collar on the opposite side, against which collar a washer surrounding the sleeve fits. The free end of a step is clamped between the head and the washer. The other end piece consists of a bolt, the bolt being provided at both ends with an external thread, whereby a head is screwed onto one external thread while the other external thread is screwed into the portion of the middle piece which is provided with an internal thread. The middle piece has an external thread at its opposite end, the thread being screwed into the internal thread of the sleeve of the other end piece. Two washers, between which the free end of a second step can be clamped, are provided around the end piece with the bolt with the external threads. This known supporting bolt has the disadvantage that it consists of eight differently shaped parts, so that its manufacture is very expensive.
According to German Utility Model 7,606,438, it is known to design the above-mentioned supporting bolt in such manner that it can be assembled from a few, simply manufactured parts. This is achieved by virtue of the fact that each retainer is in the form of a bushing with an internal thread, into which the external thread of the corresponding end piece and the middle piece can be screwed. However, this stair connection has the disadvantage that the middle piece and the end piece can be screwed into the bushing only until the ends which have been screwed in, touch. Hence, only steps of limited thickness can be gripped between the bushing and the end piece.
Austrian Pat. Nos. 230,607 and 295,112 disclose step connections wherein the supporting bolt is held at at least one of its ends by a screw anchor firmly imbedded in the steps or a threaded bushing, likewise imbedded in the concrete. This admittedly provides a simple overall design, but with the critical disadvantage that imbedding makes it impossible to completely disassemble the step connection. For example, if the firmly imbedded screw anchor is broken by excessive internal stresses which cannot be overcome in a staircase or for example if the screw anchor shifts during the casting process or the subsequent setting process, a supporting bolt connection of this type will not be usable. There is only limited possibility of repair, since it is very difficult to replace the defective part which is firmly imbedded in the concrete.